<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    body{
        height: 2000px;
    }
    .parent{

      width: 550px;
      height: 400px;
      background-color: aqua;
    }
    .child{
      width: 300px;
      height: 200px;
      background-color: coral;
      position: fixed;
      right: 100px;
      bottom: 100px;
    }
    .box{
      width: 300px;
      height: 200px;
      background-color: rgb(226, 77, 199);

    }
  </style>
</head>
<body>
  <div class="parent">
    <div class="child"></div>
  </div>

  <div class="box"></div>
</body>
</html>